Installation of tympanostomy tubes for the treatment of otitis media with effusion or in patients with recurrent events of acute otitis media, is a commonly performed surgical procedure in North America and elsewhere. In this procedure an incision is made in the tympanic membrane, fluid from within the middle ear is aspirated and a tympanostomy tube is inserted. The tubes can have various configurations and materials, and are effective in correcting the hearing loss due to the effusion as long as the tubes are in place in the ear. The materials which can be used to make tympanostoray tubes include thermoplastics such as modified elastomers and olefins, thermosets such as silicone and polytetrafluoroethylene; and metals such as stainless steel and titanium. Children with persistent middle ear effusions who do not respond to antibiotics undergo a procedure in which a myringotomy is performed in the tympanic membrane under local anesthesia. However the implantation of the tympanostomy tubes also be done under general anesthesia.
Purulent otorrhea frequently develops after tube insertion. In one study by H. G. Birck and J. J. Mravek “Myringotomy for Middle Ear Effusions,” Ann. of 0 to 1. Rhino. Laryngo., volume 85, pages 263-267 (1979), the investigators observed that 15% of children having tympanostomy tubes inserted in their ears following myringotomy developed postoperative otorrhea. In a more recent study by George A. Gates et al., “Post Tympanostomy Otorrhea,” Laryngoscope, volume 96, pages 630-634, (June 1986), the investigators observed that the incidence of tympanostomy tube induced otorrhea following myringotomy was 18%. In a clinical study performed by Balkany et al., “A Prospective Study of Infection Following Tympanostomy and Tube Insertion,” American Journal of Otology, volume 4, pages 288-291 (1983), the investigators observed an incidence of postoperative otorrhea of 19% in children receiving tympanostomy tubes with no antibiotic drops postoperatively applied. In the Balkany et al. study, the investigators found that the incidence of postoperative otorrhea was reduced to 6% when antibiotic drops were put into the patient's ear after myringotomy. In another study on the use of antibiotics after myringotomy, R. S. Baker and R. A. Chole, “A Randomized Clinical Trial of Topical Gentamicia After Tympanostomy Tube Placement,” Arch. Otolaryngology Head and Neck Surgery, volume 114, pages, 755-757 (July 1988), the investigators found that the incidence of infections in the experimental group using Gentamicin, an ophthalmic solution used as otic drops, had an incidence of infection significantly reduced by antibiotic drops.
In both the Balkany et al. and Baker et al. studies using antibiotic drops after tympanostomy, the investigators used potentially ototoxic antibiotics, namely Cortisporin and Gentamicin. Based on their frequency of use, and the lack of adverse effects noted in these studies, antibiotic drops are now used routinely to prevent postoperative otorrhea. However, thorough studies demonstrating the absence of adverse toxicological reaction in the use of antibiotic drugs for the treatment of postoperative otorrhea have not been published.
In addition to the relatively high incidence of otorrhea after myringotomy, investigators have observed children with implanted tympanostomy tubes sometimes experience bouts of otorrhea. Occasionally, the otorrhea became persistent causing some investigators to believe that the tympanostomy tubes become colonized with pathogenic bacteria.
The relatively high incidence of otorrhea after myringotomy and tympanostomy tube insertion exposes patients with persistent middle ear effusions to significant morbidity and additional treatment time and cost.
It would be desirable to utilize tympanostomy tubes whereby the incidence of otorrhea and other microbial induced infection after myringotomy and tympanostomy tube insertion could be substantially reduced without the use of antibiotics and the potential ototoxic reaction associated with the use of such drugs.
One approach for reducing bacterial infection encountered with the use of medical devices inserted into body cavities has been to apply an antimicrobial coating to the surface of the medical device. For example, U.S. Pat. No. 4,592,920 to Murtfeldt; U.S. Pat. No. 4,603,152 to Laurin et al. and U.S. Pat. No. 4,677,143 to Laurin et al. each teach applying a coating containing an antimicrobial agent such as silver oxide to the outer surfaces of medical devices such as catheters, enteral feeding tubes, endotracheal tubes and other hollow tubular devices.
U.S. Pat. No. 4,592,920 to Murtfeldt is primarily concerned with providing a surface coating of an antimicrobial metal compound on a medical device such as a catheter, but also discloses that the metal compound can be “imbedded” within the entire catheter. However, the Murtfeldt patent finds the imbedded construction to be less desirable since the antimicrobial metal compound imbedded within the side wall of the catheter has less likelihood of encountering migrating microbes and by inference is less effective than a surface coating.
U.S. Pat. No. 6,361,526 provides a tube formed from a thermoset resin containing therein between 0.5 to 15% by weight of a selected antimicrobial metal oxide compounds exemplified by silver oxide, that are capable of migrating to the sidewall surfaces of the tube. Such metal oxide-laden antimicrobial resin-based tubes are generally produced by controllably intermixing a selected metal oxide into a thermoset resin paste that is subsequently milled, then formed into a hollow tube by conventional tube-forming processes.